Chapter 11 Acids & Bases (MC2013) PDF

CHAPTER 11 Acids and Bases © 2013 Marshall Cavendish International (Singapore) Private Limited Chapter 11 Acids and Bases 11.1 Acids 11.2 Bases and Alkalis 11.3 Strength and Concentration 11.4 The pH Scale 11.5 Types of Oxides 2 ...

CHAPTER 11 Acids and Bases © 2013 Marshall Cavendish International (Singapore) Private Limited Chapter 11 Acids and Bases 11.1 Acids 11.2 Bases and Alkalis 11.3 Strength and Concentration 11.4 The pH Scale 11.5 Types of Oxides 2 11.1 Acids Learning Outcomes At the end of this section, you should be able to: define acids as substances that produce hydrogen ions in aqueous solution; describe the properties of acids and their reactions with metals, bases and carbonates; state the uses of sulfuric acid. 3 11.1 Acids Organic acids Mineral acids Tartaric acid Hydrochloric acid Citric acid Sulfuric acid Nitric acid Lactic acid 4 11.1 Acids What is an Acid? An acid is a substance that produces hydrogen ions, H+ in aqueous solution. Note that not all substances that contain hydrogen are acids. CH4 NH3 NaOH H 2O These are NOT acids. 5 11.1 Acids Is HCl Gas an Acid? HCl gas exists as covalent molecules. It is not dissolved in water so it cannot produce H+ ions. Therefore, it is not an acid. 6  11.1 Acids What is an Acid? A substance has acidic properties only when it is dissolved in water to form an aqueous solution. it ionises to produce H+ ions. Hydrogen Hydrogen chloride in chloride in an organic water ionises solvent does to give H+ not ionise. ions. This is not Hydrochloric an acid! acid is produced. 7 11.1 Acids What is an Acid? The hydrogen ions are responsible for the properties of an acid. Examples of acids: HNO3(aq) → H+(aq) + NO3–(aq) H2SO4(aq) → 2H+(aq) + SO42–(aq) CH3COOH(aq) → H+(aq) + CH3COO–(aq) 8 11.1 Acids Properties of Acids 1. Acids have a sour taste. 2. Acids turn blue litmus paper red. 3. Acids dissolve in water to form solutions which can conduct electricity. 9 11.1 Acids Properties of Acids 4. Acids react with reactive metals to form a salt and hydrogen gas. Test for H2: Use a lighted wooden splint. Flame extinguishes with a ‘pop’ sound. metal + acid → salt + hydrogen E.g. Ca, Mg, Produced when H+ in the acid is replaced Zn, Fe by a metallic ion (Na+, K+, Zn2+) or ammonium (NH4+) 10 11.1 Acids Properties of Acids Reaction of acids with metals: Example 1 magnesium + sulfuric acid → magnesium sulfate + hydrogen Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g) metal acid salt hydrogen gas 11  11.1 Acids Properties of Acids Reaction of acids with metals: Example 2 zinc + hydrochloric acid → zinc chloride + hydrogen Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) metal acid salt hydrogen gas URL 12 11.1 Acids Reaction of Acids with Lead (Pb) Not all metals react with acids to give a salt and hydrogen gas. Lead appears to be unreactive to hydrochloric acid and sulfuric acid. Why? Insoluble layer of PbCl2 or PbSO4 prevents further acid reaction. lead lead 13 11.1 Acids Properties of Acids 5. Acids react with carbonates and hydrogen carbonates to form a salt, water and carbon dioxide. carbonate + acid → salt + water + carbon dioxide E.g. Na2CO3, CaCO3, Test for CO2: ZnCO3, MgCO3 Bubbling CO2 gas through calcium hydroxide (limewater) will produce a white precipitate, calcium carbonate. 14  11.1 Acids Properties of Acids Reaction of acids with carbonates: Example 1 sodium carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g) carbonate acid salt water carbon dioxide URL 15 11.1 Acids Properties of Acids Reaction of acids with carbonates: Example 2 zinc carbonate + sulfuric acid → zinc sulfate + water + carbon dioxide ZnCO3(s) + H2SO4(aq) → ZnSO4(aq) + H2O(l) + CO2(g) carbonate acid salt water carbon dioxide 16  11.1 Acids Properties of Acids 6. Acids react with metal oxides and hydroxides to form a salt and water only. metal oxide + acid → salt + water metal hydroxide + acid → salt + water also known as bases base + acid → salt + water What is the name given to this reaction? Neutralisation 17 11.1 Acids Properties of Acids Reaction of acids with metal oxides: Example 1 zinc oxide + sulfuric acid → zinc sulfate + water ZnO(s) + H2SO4(aq) → ZnSO4(aq) + H2O(l) metal acid salt water oxide 18 11.1 Acids Properties of Acids Complete the equation: copper(II) oxide + nitric acid → copper(II) nitrate + water CuO(s) + 2 HNO3(aq) → Cu(NO3)2(aq) + H2O(l) 19 11.1 Acids Properties of Acids Reaction of acids with metal hydroxides: Example sodium hydroxide + hydrochloric acid → sodium chloride + water NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) metal acid salt water hydroxide 20 11.1 Acids Properties of Acids Complete the equation: calcium hydroxide + nitric acid → calcium nitrate + water Ca(OH)2(aq) + 2 HNO3(aq) → Ca(NO3)2(aq) + 2H2O(l) 21  11.1 Acids Role of Water in Acidity HCl(g) dissolved in an organic HCl(g) dissolved in solvent eg. water. methylated spirit No H+ ions HCl(aq) which is an acid reacts with magnesium Magnesium ribbon ribbon. does not react with magnesium Hydrogen gas is HCl. ribbon produced. 22 11.1 Acids Uses of Sulfuric Acid 1. Manufacture of fertilisers Important starting material for the production of ammonium sulfate and superphosphate, which are active ingredients in fertilisers. 2. Manufacture of detergents Concentrated sulfuric acid used to convert hydrocarbons into organic acids. Organic acids react with sodium hydroxide to produce detergents. 23 11.1 Acids Uses of Sulfuric Acid 3. As battery acid in cars Reacts with lead plates and lead(IV) oxide plates in the battery to generate electrical energy. 24 11.1 Acids Uses of Other Acids Hydrochloric acid Remove impurities such as rust or scale from metals and aluminium alloys. Phosphoric acid Added to food and beverages to give them a sour taste. Ethanoic acid Acts as food preservatives and flavour enhancer. 25 Chapter 11 Acids and Bases 11.1 Acids 11.2 Bases and Alkalis 11.3 Strength and Concentration 11.4 The pH Scale 11.5 Types of Oxides 26 11.2 Bases and Alkalis Learning Outcomes At the end of this section, you should be able to: define alkalis as substances that produce hydroxide ions in aqueous solution; describe what is meant by neutralisation and write the ionic equation for the neutralisation reaction; describe the properties of alkalis and their reactions with acids and ammonium salts. 27 11.2 Bases and Alkalis What is a Base? A base is any metal oxide or hydroxide that reacts with an acid to produce a salt and water only. base + acid → salt + water This reaction is called neutralisation. 28 11.2 Bases and Alkalis What is a Base? Examples Metal oxides Metal hydroxides sodium oxide, Na2O sodium hydroxide (NaOH) zinc oxide , ZnO zinc hydroxide, Zn(OH)2 calcium oxide, CaO calcium hydroxide, Ca(OH)2 iron(III) oxide, Fe2O3 iron(III) hydroxide, Fe(OH)3 copper(II) oxide, CuO copper(II) hydroxide, Cu(OH)2 29 11.2 Bases and Alkalis Acid-Base Reactions base + acid → salt + water Example 1 sulfuric acid + copper(II) oxide → copper(II) sulfate + water H2SO4(aq) + CuO(s) → CuSO4(aq) + H2O(l) Example 2 hydrochloric acid + sodium hydroxide → sodium chloride + water HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) 30 11.2 Bases and Alkalis What is an Alkali? An alkali is a soluble base which dissolves in water to produce OH– ions. Bases Alkalis CaO MgO Na2O NaOH FeO KOH Ca(OH)2 Cu(OH)2 NH3(aq) Fe(OH)3 ZnO Relationship between bases and alkalis 31 11.2 Bases and Alkalis What is an Alkali? Examples of alkalis: sodium hydroxide → sodium ion + hydroxide ion NaOH(aq) → Na+(aq) + OH–(aq) calcium hydroxide → calcium ion + hydroxide ion Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq) ammonia gas + water → ammonium ion + hydroxide ion NH3(g) + H2O(l) → NH4+(aq) + OH–(aq) 32 11.2 Bases and Alkalis Properties of Alkalis 1. Alkalis feel soapy and have a bitter taste. 2. Alkalis turn red litmus paper blue. 3. Alkalis react with acids to form a salt and water only. This is a neutralisation reaction. alkali + acid → salt + water 33 11.2 Bases and Alkalis Properties of Alkalis Reaction of acids with alkalis (neutralisation): Complete these word equations and construct their chemical equations: sodium hydroxide + nitric acid → sodium nitrate + water NaOH(aq) + HNO3(aq) → NaNO3(aq) + H2O(l) potassium hydroxide + sulfuric acid → potassium sulfate + water 2KOH(aq) + H2SO4(aq) → K2SO4(aq) + 2H2O(l) 34 11.2 Bases and Alkalis Properties of Alkalis Reaction of acids with alkalis (neutralisation): The ionic equation for the neutralisation reaction between and acid and an alkali is: H+(aq) + OH–(aq) → H2O(l) hydrogen ions hydroxide ions water, a neutral from acid from alkali liquid 35 11.2 Bases and Alkalis Which of these are neutralisation reactions? 1. CuO(s) + HCl(aq) → CuCl2(aq) + H2O(l) 2. ZnCO3(s) + H2SO4(aq) → ZnSO4(aq) + H2O(l) + CO2(g) 3. KOH(aq) + HNO3(aq) → KNO3(aq) + H2O(l) 4. MnO2(s) + HCl(aq) → MnCl2(aq) + H2O(l) + Cl2(g) 36 11.2 Bases and Alkalis Properties of Alkalis 4. Alkalis warmed with ammonium salts produce ammonia gas. Test for NH3: Moist red litmus paper turns blue in presence of ammonia. alkali + ammonium salt → salt + water + ammonia Contains the NH4+ ion. E.g. NH4Cl, NH4NO3, (NH4)2SO4 37 11.2 Bases and Alkalis Properties of Alkalis Reaction of alkalis with ammonium salts: Example 1 sodium hydroxide + ammonium chloride → sodium chloride + water + ammonia NaOH(aq) + NH4Cl(s) → NaCl(aq) + H2O(l) + NH3(g) 38  11.2 Bases and Alkalis Properties of Alkalis Reaction of alkalis with ammonium salts: Example 2 potassium hydroxide + ammonium sulfate → potassium sulfate + water + ammonia 2KOH(aq) + (NH4)2SO4(s) → K2SO4(aq) + 2H2O(l) + 2NH3(g) 39 URL  11.2 Bases and Alkalis Properties of Alkalis 5. Alkalis react with a solution of one metal salt to give another metal salt and metal hydroxide. alkali + salt → metal hydroxide + salt (containing metal A) (of metal B) (of metal B) (of metal A) 40  11.2 Bases and Alkalis Properties of Alkalis Example Sodium hydroxide + iron(II) sulfate → sodium sulfate + iron(II) hydroxide NaOH(aq) + FeSO4(aq) → Na2SO4(aq) + Fe(OH)2(s) 41 11.2 Bases and Alkalis Uses of Bases and Alkalis Magnesium oxide relieving gastric pain and for making refractory bricks Sodium hydroxide and potassium hydroxide used in the preparation of soap. 42 11.2 Bases and Alkalis Uses of Bases and Alkalis Calcium hydroxide – reduce acidity in soil. Ammonia solution – used in making fertilisers. 43 Chapter 11 Acids and Bases 11.1 Acids 11.2 Bases and Alkalis 11.3 Strength and Concentration 11.4 The pH Scale 11.5 Types of Oxides 44 11.3 Strength and Concentration Learning Outcome At the end of this section, you should be able to: distinguish between strong and weak acids in terms of their extent of ionisation. 45 11.3 Strength and Concentration Strong and Weak Acids A strong acid is an acid that is completely ionised in aqueous solution. Example: HCl HCl(aq) → H+(aq) + Cl–(aq) A weak acid is an acid that is only partially ionised in an aqueous solution. Example: CH3COOH CH3COOH(aq) ⇌ H+(aq) + CH3COO–(aq) 46 11.3 Strength and Concentration Strong and Weak Acids HCl is a strong acid that CH3COOH is a weak acid completely ionises in that partially ionises in aqueous solution. aqueous solution. 47 11.3 Strength and Concentration Strong and Weak Acids Do not confuse strength of an acid with the concentration of an acid! ‘Strong’ and ‘weak’ refer to the extent of ionisation of an acid. ‘Concentrated’ and ‘dilute’ tell us how much of an acid is dissolved in the solution. The strength of an acid is not affected by its concentration. 48 11.3 Strength and Concentration Strong and Weak Acids A strong acid will be fully ionised regardless of its concentration. 49 Chapter 11 Acids and Bases 11.1 Acids 11.2 Bases and Alkalis 11.3 Strength and Concentration 11.4 The pH Scale 11.5 Types of Oxides 50 11.4 The pH Scale Learning Outcomes At the end of this section, you should be able to: describe the effects of acids and alkalis on Universal Indicator; describe the use of Universal Indicator and the pH scale to test hydrogen ion concentration and relative acidity; describe the reasons for controlling the pH of the soil and the methods used to reduce excess acidity in soil. 51  11.4 The pH Scale The pH Scale Is a set of numbers from 0 to 14 It indicates if a solution is acidic, neutral or alkaline. increasing H+ = OH– Increasing H+ ions, ions, neutral OH– ions, more acidic more alkaline 52  11.4 The pH Scale The pH Scale The pH of a solution is related to the concentration of H+ or OH– present in a solution. Acids Alkalis Higher H+ concentration, Higher OH– concentration, lower OH– concentration lower H+ concentration lower pH value higher pH value 53 11.4 The pH Scale The pH Scale The pH of some common acids and bases: H2SO4 (aq) H2O(l) NaOH(aq) HCl (aq) NH3(aq) HNO3(aq) CH3COOH(aq) 54  11.4 The pH Scale pH of Some Common Substances gastric juices vinegar canned pure dilute lemon rain aqueous fizzy water HCl juice toothpastes NaOH drinks water blood detergents 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 more less less more acidic acidic alkaline alkaline NEUTRAL High H+ Low H+ Low OH– High OH– concentration concentration concentration concentration 55 11.4 The pH Scale How Do We Measure the pH of a Given Solution? Chemical compound called an indicator pH sensor attached to a data logger pH meter 56 11.4 The pH Scale Indicators Indicators are substances which show different colours in acidic and alkaline solutions. Colour change of some common indicators: Colour of indicator in Indicator Strong acidic Strong alkaline solution solution Litmus red blue Methyl Orange red yellow Screened Methyl Orange violet green Phenolphthalein colourless pink 57  11.4 The pH Scale Universal Indicator 1. Add a few drops of Universal indicator to the solution to be tested. 2. Compare the colour of the solution with the pH scale. 58 URL 11.4 The pH Scale Measuring pH pH meter measures pH electrically; more accurate and reliable; consists of a pH probe connected to a data logger. How do we use a pH probe connected to a data logger? Dip pH probe into solution to be measured. pH of solution will be displayed digitally. 59 11.4 The pH Scale pH of Soil It is important to control the pH of soil because it will affect the growth and development of plants. Potatoes grow well at Cabbages grow well at pH 5.5–6.5 pH 7.5–8.5 Most plants grow best in neutral or slightly acidic soils. 60  11.4 The pH Scale Controlling pH of Soil pH of soil may become unsuitable for plant growth due to: too much fertilisers added to the soil; environmental pollution such as acid rain. To treat acidity in soil, add: calcium oxide (quicklime); calcium hydroxide (slaked lime). This process is also known as ‘liming’. These bases neutralise the acid in the soil. What products are formed? 61 Chapter 11 Acids and Bases 11.1 Acids 11.2 Bases and Alkalis 11.3 Strength and Concentration 11.4 The pH Scale 11.5 Types of Oxides 62 11.5 Types of Oxides Learning Outcome At the end of this section, you should be able to: classify oxides as acidic, basic, amphoteric or neutral based on their metallic or non-metallic properties. 63  11.5 Types of Oxides Oxides compounds of oxygen Metallic oxides Non-metallic oxides ionic compound covalent compound metal ion and oxide ion non-metal and oxygen Basic oxides Acidic oxides Amphoteric oxides Neutral oxides 64 11.5 Types of Oxides Acidic Oxides Non-metallic oxides Often gases at room temperature Most dissolve in water to form acid React with alkalis to form a salt and water only Acidic Dissolves in water to form Name of acid oxide SO2 SO2(g) + H2O(l) → H2SO3(aq) Sulfurous acid SO3 SO3(g) + H2O(l) → H2SO4(aq) Sulfuric acid CO2 CO2(g) + H2O(l) → H2CO3(aq) Carbonic acid 65 11.5 Types of Oxides Reaction of Acidic Oxides with Alkali Example 1 sulfur dioxide + sodium hydroxide → sodium sulfite + water SO2(g) + 2NaOH(aq) → Na2SO3(aq) + H2O(l) 66 11.5 Types of Oxides Reaction of Acidic Oxides with Alkalis Example 2 carbon dioxide + sodium hydroxide → sodium carbonate + water CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O(l) Is silicon(IV) oxide an acidic oxide? Yes. It reacts with NaOH to form a salt and water only. 67 11.5 Types of Oxides Basic Oxides Metallic oxides Solids at room temperature React with acids to form a salt and water only Can be soluble or insoluble in water Dissolves in water to form Known as bases alkalis. E.g. MgO, CuO, ZnO E.g. Na2O, K2O Na2O + H2O → NaOH K2O + H2O → KOH 68  11.5 Types of Oxides Reaction of Basic Oxides with Acids Example 1 calcium oxide + nitric acid → calcium nitrate + water CaO(s) + 2HNO3(aq) → Ca(NO3)2(aq) + H2O(l) insoluble base acid salt water Example 2 sodium oxide + hydrochloric acid → sodium chloride + water Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) soluble base acid salt water 69 11.5 Types of Oxides Amphoteric Oxides React with acids to form a salt and water, behaving like a base React with alkalis to form a salt and water, behaving like an acid E.g. ZnO, PbO, Al2O3 70 11.5 Types of Oxides Salts Produced by Other Amphoteric Oxides with Alkalis Examples: Amphoteric oxide Salt produced in NaOH Aluminium oxide (Al2O3) Sodium aluminate (NaAlO3) Lead(II) oxide (PbO) Sodium plumbate (Na2PbO2) 71 11.5 Types of Oxides Reaction of Zinc oxide with Acid/Alkali zinc oxide + hydrochloric acid → zinc chloride + water ZnO(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l) What property does ZnO show here? zinc oxide + sodium hydroxide → sodium zincate + water ZnO(s) + 2NaOH(aq) → Na2ZnO2(aq) +H2O(l) What property does ZnO show here? 72 11.5 Types of Oxides Neutral Oxides Insoluble in water Show neither acidic nor basic properties E.g. H2O (water) NO (nitric oxide) Note that they are CO (carbon monoxide) also monoxides. 73 Chapter 11 Acids and Bases Concept Map 74 Chapter 11 Acids and Bases Concept Map 75 Chapter 11 Acids and Bases Concept Map 76 Chapter 11 Acids and Bases The URLs are valid as at 15 October 2012. Acknowledgements (slide 1) yellow lemons © Abhijit Tembhekar | Wikimedia Commons | CC BY 2.0 (http://creativecommons.org/licenses/by/2.0/deed.en) (slide 4) grapes © Stuuf | Wikimedia Commons | Public Domain (slide 4) oranges © Benjamin D. Esham | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) (slide 4) yogurt © Erud | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) (slide 4) hydrochloric acid © Bartłomiej Bulicz | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) 77 Chapter 11 Acids and Bases Acknowledgements (slide 4) hydrochloric acid © Walkerma | Wikimedia Commons | Public Domain (slide 4) nitric acid fuming © W. Oelen | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) (slide 4) acidic drain cleaner containing sulfuric acid © DualDoomsdays | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) (slides 58–59) © Marshall Cavendish International (Singapore) (slide 60) potatoes © Tahir mq | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) (slide 60) cabbage © Evelyn Gunn | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) 78